The present invention relates to a process for the recovery of value metals, and in particular cobalt, nickel, molybdenum, vanadium and aluminum, from spent and roasted crude-oil sulfur-extraction catalyst wastes by leaching finely-divided burnt leavings at an elevated temperature and by separating valuable substances from the solution.
A considerable amount of sulfur dioxide passes into the environment when sulfur-containing oil products are used. In order to diminish the sulfur emission it is necessary in oil refineries to remove most of the sulfur in crude-oil in connection with the refining of crude-oil. For the extraction of sulfur, hydrogen is directed at a suitable pressure and temperature through crude-oil in the presence of catalysts. The sulfur present in the oil reacts with the hydrogen, thereby forming gaseous hydrogen sulfide, which is directed out of the reaction system and recovered. The catalysts used are mainly aluminum oxide based materials in which the active constituents are cobalt and molybdenum or nickel and molybdenum. During the extraction of sulfur, some of the vanadium and nickel present in the oil passes into the catalysts, which become enriched with these metals, the catalysts gradually losing their catalytic activity.
In addition to the aluminum oxide base the spent catalysts thus contain cobalt, nickel, molybdenum and vanadium. All these constituents are valuable, and it is advisable to aim at recovering all of them during the reprocessing of the spent catalysts.
It is an established practice to subject the catalyst wastes to an oxidizing roasting at below 600.degree. C. in order to remove the volatiles concentrated in them, hydrocarbons, carbons, and some of the sulfur and compounds of sulfur. Especially in connection with plants in which sulfidic concentrates are roasted or smelted, such a pre-treatment of spent catalysts by roasting is simple to carry out, since the flue gases can easily be directed into SO.sub.2 -bearing roaster or smelting-plant gases.
The burnt leavings are usually crushed and ground before further processing.
The German Pat. No. 23 16 837 discloses a multiple-stage process for the recovery of the valuable elements present in catalyst waste. Calcined catalyst waste is roasted in the presence of sodium chloride, whereafter the molybdenum and vanadium are leached in water and separated. The cobalt, nickel and aluminum remaining in the precipitate are trated during the subsequent stage by means of a sodium hydroxide solution, whereby aluminum is obtained in the solution and is precipitated out from it as aluminum hydroxide after separation. The cobalt and nickel are recovered from the filtration precipitate by known methods. The process is a multiple-stage process and, owing to a high consumption of reagent, expensive. Also, it is necessary to treat aluminum oxide, the main constituent of the catalyst waste, in several process stages before it is obtained in solution form and further recovered. The treatment of large amounts of precipitates, of course, complicates the various process stages and increases the cost.
In the process according to U.S. Pat No. 4,087,510 one process stage has been eliminated as compared with the above, by calcining the catalyst waste directly with sodium carbonate without the normal oxidizing roasting, whereby the vanadium and molybdenum are brought to a water-soluble form and can be separated as above.
The aluminum, cobalt and nickel remaining in the precipitate can be recovered by known methods, for example as instructed in the German Pat. No. 23 16 837.
In addition, several processes are known in which only one or some of the valuable elements of the catalyst waste are recovered, the aluminum oxide or aluminum hydroxide which constitutes the base of the catalyst waste remaining in the waste. When aluminum-based Co-, Mo-, V- and Ni-containing catalyst wastes are leached for the recovery of Co, Mo, V and Ni, aluminum dissolving and reprecipitation problems come up.
For a high leaching yield of the valuable metals it is, however, necessary also to leach the aluminum which constitutes the base of the catalyst.
The object of the present invention is to provide a process by which it is possible to bring in a single stage the cobalt, nickel, molybdenum and vanadium of the catalyst waste into solution form and simultaneously the aluminum into the solid phase. The metals in the solution are recovered by known methods. The invention leads to a simple and reliable process by which, furthermore, considerable savings are achieved in equipment, as compared with previous processes.